Linux

7.10    Variables in Bash Scripts

I have already provided some initial information on dealing with variables in Section 7.7. This section covers other aspects of variable management that are particularly relevant to shell programming. In detail, it is about the scope of variables, about some variables predefined in bash (e.g., $* or $?), about the mechanism of parameter substitution for analyzing and processing strings in variables, and finally about the input of variables in shell programs.

7.10.1    The Scope of Variables

To run a command or a script, bash creates a new process with its own PID number. This is an internal Linux number to identify and manage the process. Of the variables, only those declared as environment variables (export ...